This invention relates to a feature recognition system and more particularly to a system for processing transient submarine signals which occur in the presence of signal-like noise and for recognizing certain relatively invariant features exhibited by the submarine signals and not by the noise signals.
In the field of submarine detection and recognition, magnetic anomaly detection (MAD) devices and techniques have long been utilized. Basically, MAD is an airborne system employing magnetometer elements which sense the presence of a submerged submarine by measuring the small distortion in the earth's magnetic field caused thereby. This technique is an exacting one as the earth's magnetic field intensity may be on the order of 10,000 times stronger than that of the submarine. Additionally, the high altitudes of the aircraft, or more exactly the long slant ranges to the submarine, cause the signals from the submarine to virtually disappear into the noise background. This noise is derived from a multiplicity of sources as from, for example, the magnetometer sensing element itself, the magnetic and electrical equipments of the aircraft, large magnetic fields external to the aircraft such as geologic mineral deposits beneath the ocean floor, and other phenomena.
Due to these many noise sources and the distance between sensor and submarine, the submarine signal is either completely disguised by the noise such that it cannot be recognized therefrom or the noise signals themselves produce a response similar to the submarine signals such that false recognitions are effectuated.
Prior art systems incorporated a trained human operator who memorized features or patterns known to be representative of the signature of a submarine and whose function it was to visually recognize and extract these submarine signals from data displayed before him. The accuracy of such a technique was relatively low and varied with the individual operator. In addition, all of the operators fatigued with time thus further decreasing accuracy. The result was that many false alarms were indicated and many actual targets were entirely missed.
Thus there arose a need for a system capable of automatically and electronically recognizing and detecting, with a high degree of accuracy and reliability, submarine signals occurring in the presence of signal-like noise.